For numerous years, the majority of transportation vehicles (planes, trains, tramways, cars . . . ) have been provided with individual lighting systems. This individual lighting, still known as a reading light, is created by a lamp equipped with an incandescent bulb. These reading lights are powered directly by the operating voltage of the vehicle. The main disadvantage of such system resides in the fact the incandescent bulbs have a limited life time and require regular changing, which increases the cost of maintenance of such systems and has an adverse effect on the comfort of passengers. To overcome these disadvantages, it has been suggested to replace such lighting devices with light-emitting-diode lighting systems. Indeed, light-emitting diodes, commonly known as “LEDs”, have a greatly increased life time when compared to incandescent bulbs and their power consumption is far below that of incandescent bulbs. The power supply of such reading lights is generally a remote power supply used for many reading lights simultaneously. Although the maintenance costs of this type of reading light is far below that of the prior art systems, there are many issues with this configuration. For instance, in the event of a power outage, all reading lights connected to this remote power supply stop operating, and the replacement of incandescent-bulb reading lights with LED reading lights cannot be done without modification to the power supply wiring of the vehicle. The connection of the LED reading light in direct replacement of an incandescent light is impossible because of an incompatibility in voltages. In effect, the voltage of the vehicle wiring, such as a train car, is too high with respect to the maximum acceptable voltage set for a LED, and it is therefore necessary to transform this voltage and consequently modify the vehicle wiring. This involves a complex and burdensome intervention, as well as important costs.
As is well known, LED lamps often operate under two states, either off or on at full brightness power. Accordingly, a user can only turn on or off a reading light and cannot vary the brightness, but can modify the orientation of the luminous flux so as to direct the flux to avoid disturbing other passengers of the vehicles. In United States Publication No. 2006/0146553 (by Zeng et al.), a solution to this problem is suggested in the form of a dimmable reading light. This dimmable reading light with emergency lighting capability is used with vehicles, such as planes. This reading light has a housing for attaching the reading light to an interior portion of the vehicle, and a field replaceable unit. The field replaceable unit comprises a power module including a power interface for receiving operational power from a power source, a light module including a plurality of LEDs, and a control module that includes a control interface for receiving a user input signal so that the control module can vary a light intensity that is output from the plurality of LEDs according to the user input signal. This power module may be equipped with power protection means, such as a fuse, a relay . . . for protecting the reading light. The power module may comprise power conversion means producing input power adapted for LEDs and for the control module. The power and control modules are provided on a printed circuit board positioned inside the replaceable unit, but either one of the modules can be positioned outside of the replaceable unit. The printed circuit board has a processor such as a microprocessor. Moreover, the field replaceable unit may include a temperature sensor allowing an increase in the life time thereof. In a given embodiment, the temperature sensor is on the printed circuit board to measure the temperature of the heat sink so as to protect the processor. The power module may have two interfaces and may include a dc/dc converter and a voltage regulating means.
In United States Publication No. 2002/0145871 (by Yoda), there is suggested a cabin light with a housing having a spherical side surface rotatably installed in a panel. A printed circuit board has LEDs, each provided with a reflector concave portion, the portions forming a reflector unit. A connector is connected at a tip end to a cord for feeding electricity to the LEDs and, on another side to pins that protrude from a cylindrical element made of a conductive metal, at the end of which a feeding terminal is provided. This above-described lamp is well suited for interchangeability with cabin lights using incandescent bulbs. A heat sink is provided on the rear face of the printed circuit board. This device comprises condenser portions and, by way of the reflector concave portions and fish-eye steps, the diffused light is suitable for reading. A controlled distribution of the light is obtained by controlling the light by way of a condenser and diffuser means. Each reflector unit is made of concave aluminum walls that are eventually filled with transparent resin defining a columnar recess portion with a convex surface to condense the luminous flux of the LED.
The above-described reading lights always use a plurality of LEDs for each single lighting unit. One of the references describes the control of the brightness intensity of the set of LEDs, and the other reference teaches the control of the luminous flux of each LED so as to define a condensed beam projector producing a diffused light illuminating a zone of about 50 cm in diameter at about 1 m from the surface of the lamp. Therefore, it is noted from these reading lights that a given amount of LEDs is required each time to provide suitable lighting.